Diffusion transfer production of reflection positive with dialdehyde in receptive stratum

ABSTRACT

PHOTOGRAPHIC PRODUCTS FOR FORMING A COMPOSITE PRINT VIEWABLE AS A POSITIVE SILVER IMAGE, INCLUDING A SILVER HALIDE EMULSION LAYER, AN OPACIFYING MATERIAL IN THE EMULSION LAYER AND/OR IN AN OVERLYING LAYER, AND AN OUTER LAYER COMPRISING A SILVER-RECEPTIVE STRATUM, WHEREIN THE SILVER-RECEPTIVE STRATUM INCLUDES A REAGENT WHICH UPON APPLICATION OF AN AQUEOUS ALKALINE PROCESSING LIQUID WILL EFFECT A HARDENING OF THE SILVER-RECEPTIVE STRATUM AT SOME TIME DURING OR AFTER IMAGE FORMATION BUT WHICH WILL NOT ADVERSELY RETARD TO ANY NOTICEABLE EXTENT THE ABSORPTION RATE OF THIS LIQUID THROUGH THE STRATUM.

June 22, 1971 L. c. FARNEY 3,586,502 DIFFUSION TRANSFER PRODUCTION OF REFLECTION POSITIVE WITH DIALDEHYDE IN RECEPTIVE STRATUM Filed April 22, 1968 |4- \JSILVERRECEPTIVE STRATUM |2-: TRANSLUCENT LIGHT-SENSITIVE LAYER IO\ \SUPPORT FIG. I

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SILVER-RECEPTIVE STRATUM TRANSLUCENT OUTER LAYER TRANSLUCENT LIGHT-SENSITIVE LAYER SUPPORT SILVER-RECEPTIVE STRATUM TRANSLUCENT LAYER LIGHT-SENSITIVE LAYER SUPPORT INVENTOR. (xZma wl 6 egg/m7 EIww n MW ATTORNEYS United States Patent ()1 fice 3,586,502 Patented June 22., 1971 DIFFUSION TRANSFER PRODUCTION OF RE- FLECTION POSITIVE WITH DIALDEHYDE IN RECEPTIVE STRATUM Leonard C. Farney, Melrose, Mass., assignor to Polaroid Corporation, Cambridge, Mass. Filed Apr. 22, 1968, Ser. No. 723,004 Int. Cl. G03c 5/54 US. Cl. 96-29 9 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF INVENTION The copending application of Edwin H. Land, Ser. No.

519,995 and the copending application of Edwin H. Land and Leonard C. Farney, Ser. No. 519,884, both filed Jan. 11, 1966, describe and claim photographic products and processes for forming a composite print comprising a negative image and a positive image, the print being viewable as a positive reflection print without separation of the respective images.

As is disclosed in these applications, a photographic film assembly including a layer containing a light opacity-providingmaterial is exposed, e.g., to a light source on the same side of the support for the film assembly as the layer of opacity-providing material, and is then processed to form a negative image and a positive transfer image in a stratum situated above the layer of opacity-providing material. This material is present in an amount sufficient for masking effectively the negative image but not in an amount suflicient to preclude photoexposure of the lightsensitive material in the film assembly, so that there is formed a composite print which contains both a negative and a positive image but which is viewable by reflection as a positive reproduction of the original subject matter.

" The opacifying material further serves to provide the background for viewing the print by reflection.

In application Ser. No. 519,995, the layer of opacify-.

ing material is situated over a layer containing a lightsensitive silver halide emulsion; while in application Ser.

'No. 519,884, the opacifying material is situated in the same layer as the emulsion and may also be present in a second layer over the layer containing the silver halide emulsion. A silver-receptive stratum comprising a suitable matrix containing silver-precipitating nuclei may be provided over the opacifying material in the products contemplated by these copending applications.

In preparing the composite print, the outer surface of the silver-receptive stratum of the exposed element is contacted with an aqueous medium which may contain an alkaline material, a silver halide developing agent and a silver halide solvent, and this aqueous medium diffuses through to the silver halide emulsion layer to develop the negative image and in known manner to form an imagewise distribution of a soluble silver complex which is transferred, at least in part, by diffusion, to the silver-receptive stratum where it is reduced to provide a positive silver transfer image. The above-named ingredients may be contained initially in the aqueous medium, or in lieu thereof, any or all of them may be contained initially in one of the layers of the film unit, in which event a solution of the same is obtained upon permeation of the aqueous medium. The aqueous medium may also include other reagents performing specific desired functions, e.g., preservatives, antifoggants, etc. and may also include a viscous film-forming reagent.

The aforementioned procedures are of particular use in the field of document duplication and they may be employed in conjunction with suitable apparatus for pro viding one or more copies of the original in a rapid and efficient manner.

In the aforementioned film units, one preferred matrix for the silver-receptive stratum comprises gelatin or a mixture of colloidal silica and gelatin, the ratio of gelatin to silica being on the order of from about 1:1 to about 1:10. However, with such a matrix there is a tendency for some loss of silver in the positive silver transfer image imparted to this stratum due to What has been termed image rub-01f. In other words, such a matrix is unduly sensitive to moisture so that if the resulting print is subjected to moisture and particularly if it is rubbed while so subjected to moisture, the stratum containing the image tends to be removed at least in part.

One possible solution to the problem of image rub-off would be to incorporate some additive in this stratum which would serve to harden it prior to use. However, such an addition prior to image formation would reduce the absorption rate or, stated another way, increase the time required for absorption of the processing liquid applied to the surface of this stratum to develop the exposed film unit. This would be undesirable since the more rapid the absorption or permeation of the processing fluid, the less is the tendency for staining of highlight areas of the print caused by aerial oxidation, particularly in the presence of elevated temperatures such as may be employed for drying of the print. One the other hand, applying an additive for hardening and protecting the image after processing, e.g., by coating the print, requires an after-treatment which should ideally be avoided.

The present invention is directed to the prevention of image rub-off without the disadvantages of impairment of absorption rate and/or the requirement of aftertreatment.

SUMMARY OF THE INVENTION absorption rate is not reduced, the requisite hardening taking place some time during or'after image formation. BRIEF DESCRIPTION OF DRAWING FIG. 1 is a partially schematic, partially enlarged fragmentary sectional view illustrating one film unit to which this invention is directed;

FIG. 2 is a similar view of another film unit; and

FIG. 3 is a similar view of still another film unit.

DESCRIPTION OF PREFERRED EMBODIMENT In the preferred embodiment, the additive comprises a dialdehyde, preferably a polymeric dialdehyde such as a dialdehyde starch, which in the presence of alkali will cross-link or tan the gelatin in the matrix.

As was mentioned previously, this invention relates to novel products and processes for preparing a composite print viewable as a positive reflection print and, more particularly, to photographic products and processes such as are described and claimed in the aforementioned copending applications Ser. Nos. 519,995 and 519,884 wherein a macroscopic pigment is included in the silverreceptive stratum.

A primary object of this invention, therefore, is to provide novel products and processes of the foregoing description.

A further object is to provide novel products including a light-sensitive silver halide emulsion, an opacifying material in the same or an overlying layer, and an outer silver-receptive stratum including a reagent of the foregoing description.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the several steps and the relation and order of one or more of such steps with respect to each of the others, and the product possessing the features, properties and the relation of elements which are exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawing.

The invention will be more readily understood by reference to the accompanying drawing.

The photographic products to which this invention is directed include a light-sensitive silver halide emulsion layer, a layer of opacity-providing material which may be in the same layer as the emulsion, in an overlying layer, or both, and an outer silver-receptive stratum including silver precipitating nuclei providing a vigorous silver precipitating environment for reduction of a soluble silver complex transferred thereto to image silver.

In the embodiment shown in FIG. 1, the film unit comprises a support 10, preferably opaque, having thereon a layer 12 including a light-sensitive silver halide emulsion and an opacifying material, and a silver-receptive stratum 14.

In the embodiment shown in FIG. 2, an additional layer 16 of opacifying material is provided between layer 12 and stratum 14.

The products shown in FIGS. 1 and 2 are described and claimed in the aforementioned copending application Ser. No. 519,884.

In the embodiment shown in FIG. 3, the support contains a light-sensitive silver halide emulsion layer 12a, and the opacifying material is contained in a layer 16 situated between layer 12a and silver-receptive stratum 14. This last-named embodiment is described and claimed in the aforementioned copending application Ser. No. 519,995.

In all of these embodiments, the film unit is selectively exposed, e.g., through the outer stratum 14, to provide a developable or latent image in the photosensitive layer. At some time thereafter, the element is developed by contacting the surface of stratum 14 with an aqueous medium which either contains the necessary ingredients for development or forms a solution of these ingredients after contact. In other words, the aqueous medium may comprise an aqueous processing composition including an alkaline material, a silver halide developing agent and a silver halide solvent or, in lieu thereof, any or all of these ingredients may be contained initially in one or more layers of the film unit. In either event, the aqueous medium permeates through stratum 14 (and any additional intermediate layers) to the photosensitive layer (12 or 12a) to initiate development. In known manner, exposed and developable silver halide is reduced to form a negative image while an imagewise distribution of a soluble silver complex is formed in terms of unexposed or undeveloped areas of the emulsion. This imagewise distribution is transferred, at least in part, to stratum 14 where it is reduced to image silver to impart thereto a positive silver transfer image. The resulting composite print comprising the developed'negative image and the overlying positive silver transfer image is viewable without separation as a positive silver reflection print, owing to the ability of the opacifying material to mask efiectively the negative image.

Support 10 may be made of any of the materials heretofore used for such purposes, e.g., paper, a celluluose ester, etc. and is preferably opaque.

Layer 12 includes a light-sensitive silver halide emulsion, preferably a gelatino silver halide emulsion which upon development will form a negative silver image of relatively low density or covering power. It may, for example, be a mixed halide emulsion, e.g., a silver iodobromide or chloroiodobromide emulsion, which possesses a relatively high speed as compared, for example, with the speed of silver chloride emulsions.

The opacifying material, which is preferably colorless or white, is at least permeable to, but substantially insoluble in the aqueous processing medium. As examples of useful opacifying materials, mention may be made of finely divided titanium dioxide, calcium carbonate, magnesium oxide, barium sulfate, etc. or mixtures of such materials.

Layer 16 of the embodiments shown in FIGS. 2 and 3 may comprise one or more of the aforementioned pigments dispersed in a suitable matrix such as gelatin.

The silver-receptive stratum provides a vigorous silverprecipitating environment and comprises, in addition to the macroscopic pigment of this invention, at least one of the known silver-precipitating agents dispersed in a continuous vehicle or matrix. In the embodiment contemplated by this invention, this vehicle or matrix comprises gelatin or a mixture of gelatin and a siliceous material, e.g., one containing, in colloidal condition, oxides of silicon, particularly those in the form of silica acids, such as Syton (trademark of Monsanto Chemical Co. for a milky-white, stable 15% colloidal dispersion of silica in water); Santocel (trademark of Monsanto Chemical Co. for a light-weight porous silica aerogel from which the water has been removed by a process that does not destroy the original gel structure); or Ludox (trademark of E. I. du Pont de Nemours & Co. for an aqueous colloidal sol containing approximately 30% Si0 with less than ).5% Na 'O as stabilizer), etc., or a mixture of such materials. The ratio of gelatin to silica, as heretofore lllOitbd, may be on the order of from about 1:1 to about As examples of silver-precipitating nuclei, mention may be made of those heretofore known in the art, e.g. heavy metal sulfides and/or selenides, the colloidal noble lnetals, organic thio compounds, etc. The layers or strata described above and shown in the illustrative drawing may also contain additional ingredients performing specific desired functions, as will be appreciated. For example, any or all of the ingredients essential to development may be contained in one or more of these layers, as heretofore noted.

In accordance with the present invention the silverreceptive stratum further includes an effective amount of a reagent which will harden or tau the gelatin in this stratum at some time subsequent to contact by the alkaline processing fluid but will not adversely affect the absorptlon rate of this fluid through the stratum, at least to any noticeable extent. This hardening or tanning materially reduces or obviates any existent problem of rub-ofi or reduction in silver density.

A preferred reagent is a dialdehyde, preferably a polymeric dialdehyde. As examples of useful dialdehydes mention may be made of succinaldehyde and the class of polymeric dialdehydes known as dialdehyde starches: e.g., Sumstar-S (Trademark of Miles Chemical Co. for a water-dispersible dialdehyde starch and Dasol A (trade-. mark of Miles Chemical Co. for a water-soluble dialdehyde starch.

These materials are understood to contain recurring groups of the formula:

The amount of reagent such as the aforementioned dialdehydes employed in the silver-receptive stratum will vary according to the composition of the stratum, as will be appreciated by those skilled in the art, and the present invention accordingly contemplates use of effective amounts of the reagent, i.e., amounts suflicient to provide at least significant decrease in image rub-off. Preferably, the amount employed should not be so great or excessive as to affect, at least to any appreciable extent, the absorption rate of the processing fluid.

Optimum amounts between the above limitations may be readily determined for any given system by those skilled in the art in the light of this disclosure. For example, the lower limits can be determined by preparing a composite print, moistening the print, rubbing vigorously, and observing the amount of loss of silver density,

at a ratio to gelatin of 1:50. No increase inabsorption time was noted.

EXAMPLE 3 loss of density was noted in the print of Example 2.

if any. If such a loss is too great to be desirable, greater amounts can be employed to provide the desired results. The preferred upper limit can be calculated by test samples in which the aborption rate is calculated by applying the processing fluid and observing the time required for disappearance of surface gloss on the film unit.

In a typical product contemplated by this invention, the ratio of reagent to gelatin required to obtain the desired hardening effect may be on the order of from about 1:5 to about 1:75, a preferred ratio being on the order of about 1:10 to about 1:50.

It has heretofore been known that polymeric aldehydes such as the aforementioned dialdehyde starches will crosslink or tan gelatin. With Sumstar-S and Dasol A it has been stated that optimum cross-linking occurs at a pH of 6-8 while overtanning occurs at a pH of 9-14. Since a typical silver-receptive stratum falls within the first-named pH range and a typical alkaline processing fluid within the second, it is surprising that such a reagent could be incorporated in this stratum prior to photographic use without adversely affecting the absorption rate of the fluid. Hence, the essence of the invention is the discovery that by this addition an in situ hardening can be accomplished at some time subsequent to permeation of the processing fluid, i.e., during or subsequent to image formation, to achieve the desired advantage of materially reducing or obviating image rub-ofl without increasing the absorption time and the resulting disadvantages caused by this slower absorption rate.

The following examples show by way of illustration and not by way of limitation the practice of this invention.

EXAMPLE 1 A film unit as shown in FIG. 1 was prepared in the manner disclosed in the aforementioned application Ser. No. 519,884. Layer 12 included a gelatino silver chloroiodobromide emulsion and titanium dioxide. Silverreceptive stratum 14 comprised a silver-precipitating environment containing colloidal gold dispersed in a matrix of gelatin and colloidal silica, the ratio of gelatin to colloidal silica being about 1:3. Silver-receptive stratum 14 was applied over the translucent emulsion layer toprovide a calculated coverage of mgm. of gelatin and 90 mgm. of silica per square foot of surface area. This film unit was exposed and developed in the described manner to provide a composite print viewable as a positive silver reflection print.

EXAMPLE 2 The procedure of Example 1 was repeated except that Dasol A was included in the silver-receptive stratum From the foregoing description and illustrative examples it will be noted that the present invention provides significant improvement in obviating the problem of rubofl and none of the disadvantages one might anticipate due to longer absorption times.

The present invention may be employed in conjunction with the invention described and claimed in the copending application of Leonard C. Farney and Richard Haberlin, Ser. No. 723,002 wherein a macroscopic pigment is included in the silver-receptive stratum and/ or the invention described and claimed in the copending application of Edgar W. Miller and Harry A. Smith, Ser. No. 723,003

wherein an additive comprising aluminum stearate is incorporated in this stratum, both of which cases are filed concurrently.

Since certain changes may be made in the above product and process without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. In a photographic product for preparing a composite print viewable as a positive reflection print, said product comprising a layer containing a light-sensitive silver halide emulsion, a light opacity-providing material in said layer or in an overlying layer and a silver-receptive stratum including silver-precipitating nuclei dispersed in a macroscopically continuous matrix including gelatin, said light opacity-providing material being present in an amount suflicient for masking effectively a negative image formed in said emulsion layer by exposing said photographic product and developing said exposed product by applying an aqueous processing fluid to the surface of said silver-receptive stratum to form said negative image and a positive image in said silver-receptive stratum, whereby said composite print is viewable without separation as a positive silver reflection print; the improvement which comprises including in said silver-receptive stratum an effective amount of a dialdehyde hardening reagent for hardening said stratum at some time subsequent to permeation of said fluid through said stratum.

2. A product as defined in claim 1 wherein said reagent comprises a polymeric dialdehyde.

3. A product as defined in claim 2 wherein the ratio of dialdehyde to gelatin in said silver-receptive stratum is from about 1:5 to about 1:75.

4. In a photographic product for forming a composite print in which a positive image is formed in a stratum over a negative image, said composite print being viewable as a positive reflection print without separation of said two images, said product comprising a light-sensitive silver halide emulsion, said layer further including a light opacity-providing material, and a silver-receptive stratum above said emulsion layer said silver-receptive stratum comprising silverprecipitating nuclei dispersed in a continuous matrix comprising gelatin and colloidal silica, said opacity-providing material being present in an amount suflicient for masking effectively a silver image formed in said layer by exposing said photographic product and developing said exposed product by applying an aqueous processing fluid to the surface of said silverreceptive stratum to form said negative image in said layer and a positive transfer image in said silver-receptive stratum, the amount of said material being insuflicient to preclude photoexposure of said silver halide, said material further being capable of providing a background for viewing said composite print by reflected light as a positive image; the improvement which comprises including in said silver-receptive stratum an effective amount of a dialdehyde hardening agent.

5. A product as defined in claim 4 wherein said dialdehyde is a polymeric dialdehyde.

6. A product as defined in claim 4 wherein the ratio of gelatin to colloidal silica in said silver-receptive stratum is from about 1:1 to about 1:10.

7. A product as defined in claim 6 wherein said dialdehyde is a dialdehyde starch, the ratio of said starch to said gelatin in said stratum being from about 1:10 to about 1:50.

8. A process for preparing a positive silver transfer image comprising exposing a product as defined in claim 1 to provide a developable image; applying an aqueous processing fluid to the surface of said product; rapidly permeating said fluid through said silver-receptive stratum to said emulsion layer to develop said exposed emulsion and to form an imagewise distribution of a soluble silver complex in terms of unexposed areas of said emulsion; transferring said imagewise distribution, at least in part, by diffusion, to said silver-receptive stratum where it is reduced to impart thereto a positive silver transfer image; and at some time subsequent to permeation of said fluid hardening said silver-receptive stratum in situ to protect said positive silver transfer image from image rub-off.

9. In a process wherein a photographic product ineluding a layer containing a light-sensitive silver halide emulsion and a light opacity-providing material and an overlying silver-receptive stratum comprising silver-precipitating nuclei dispersed in a matrix comprising gelatin and colloidal silica is exposed to form a developable image and said exposed product is developed by contacting the surface of said silver-receptive straturn with an aqueous alkaline fluid, said fluid permeating through said stratum to develop said image and to impart to said silver-receptive stratum a positive silver transfer image, said transfer image being viewable by reflected light, the improvement which comprises incorporating in said silver-receptive stratum before exposure of said product a polymeric dialdehyde in an amount suflicient to harden said matrix at some time after said permeation.

References Cited UNITED STATES PATENTS 3,057,723 10/1962 'Jeifreys et a1 9699 3,369,901 2/1968 Fogg et a1. 9676 NORMAN G. TORCHIN, Primary Examiner W. H. LOUIE, JRQAssistant Examiner US. Cl. X.R. 9676 

